Electric arc furnaces are characterized by three electrodes immersed in the molten metal. Each electrode has a holder which in the past has often been in the form of a copper casting, with cooling coils embedded in the casting. Copper is employed because of its low electrical resistivity and high heat conductivity. The cooling coils have generally been fabricated from steel, copper and/or Monel. The coils are placed in a casting mold and then the copper is cast around the cooling coils. However, the cast copper does not bond itself to the coils; and so there remains a small air space between the coils and the copper casting. This space, along with the coil material itself, impedes the flow of heat between the casting and the water, and so the cooling of such holders has been inadequate and their current rating and life expectancy have been correspondingly unsatisfactory.
It is known to make such bowls from a single copper slab milled with water passageways in its surface. These passageways are then closed by strips welded over the passageways. An example of this construction is shown in U.S. Pat. No. 4,110,548, the disclosure of which is incorporated herein by reference.
However, the construction shown in that patent has a number of disadvantages. In the first place, the plate has to be pre-heated and subjected to a welding opertion to apply the closure strips. Each weld thus provided, generates a region of weakness which also has undesirable electrical and thermal properties. Moreover, the welds often leak due to the metallurgical change that has taken place during preheating and welding of the strips. This metallurgical change results in grain growth and grain boundary movement; and failure tends to be encountered due to creep, fracture and fatigue.
As the channels or passageways in the construction of that patent are formed by milling, they are rectangular in cross-sectional configuration. Accordingly, cracks tend to form at the corners. Furthermore, an undesirably large quantity of material must be removed from the patented construction, which lowers the impact strength of such a design. Still further, the patented design has an undesirably high electrical resistivity.
Still further, the construction of that patent suffers in that the thickness of the walls of the passageway on the outer side thereof is undesirably small. The water passageways accordingly are not well protected from the arcing that frequently occurs between closely spaced electrode holders in an electric arc furnace.
Finally, the rectangular configuration of the water passages in the construction of that patent, does not provide uniform heat exchange between the water and the metal through which it flows.
It is accordingly an object of the present invention to provide a method for making an electrode holder of the type described, which will result in a holder having improved heat exchange characteristics between the cooling water and the metal through which it flows.
Another object of the present invention is the provision of a method for making such an electrode holder, which will be metallurgically homogeneous.
Still another object of the present invention is the provision of a method for making such an electrode holder, which will be strong and leakproof.
It is also an object of the present invention to provide a method of making such an electrode holder, which will have relatively low electrical resistivity.
Finally, it is an object of the present invention to provide a method for making such an electrode holer, which will be simple and easy to practice with dependable results.